1. Field of the Invention
This invention relates to an apparatus for detecting a pixel correlation and generating an interpolation signal for a digital television signal contained in a television signal processing device used, for example, in a high quality digital television system.
2. Description of the Related Art
In a sequential scanning conversion circuit for converting an interlace television signal into a non-interlace television signal, for example, a scanning line interpolating process is effected. This process can be accomplished using either double-scanning type interpolation or upper-lower signal addition type interpolation.
In the case of double-scanning, an interlace signal is supplied to a delay circuit having a delay time corresponding to one horizontal scanning period. The output signal of the delay circuit is used as an interpolation signal which is combined with the input interlace signal by means of a synthesizing circuit which in turn supplies a non-interlace signal to a processing circuit.
In the case of upper-lower signal addition, an input interlace signal is supplied to a first delay circuit and a first constant multiplier having a coefficient of 1/2. An output signal of the first delay circuit is supplied to a second delay circuit and a second constant multiplier having a coefficient of 1; the first and second delay circuit each have a delay time corresponding to one horizontal scanning period. An output signal of the second delay circuit is supplied to a third constant multiplier having a coefficient of 1/2. Output signals of the first, second, and third constant multipliers are added together in an adder. As a result, the adder obtains an interpolation signal which is combined with an input interlace signal in an synthesizing circuit, which in turn supplies a non-interlace signal to a processing circuit.
The double-scanning type interpolation signal generating circuit and the upper-lower signal addition type differ in the vertical filtering characteristic of the derived interpolation signal, with the cut-off frequency in the upper-lower signal addition type circuit being lower than in the double-scanning type circuit. Hence, when a vertical high-frequency component, which has a vertical spatial frequency of 525/2, is supplied to both types of circuits under the same conditions, the upper-lower signal addition type circuit attenuates the high-frequency component more than the double-scanning type one.
The high-frequency component will appear as an aliasing component in the image formed from the television signals and interpolation signals. Therefore, it would be desirable to use the upper-lower signal addition type interpolation signal generating circuit which attenuates the high-frequency component more than the double-scanning type. As described above, less aliasing components will appear in the upper-lower signal addition type method than in the double-scanning type method. On the other hand, the upper-lower signal addition type method has a problem in that vertical high frequency components are attenuated.
A high-quality image may be obtained from television signals and interpolation signals which are represented pixels, provided that each interpolation signal has been generated by interpolating two television signals which are represented very similar pixels. Nonetheless, it is desirable that a processing device be manufactured and used which is simple in structure and operates at high speed to detect the similarity between any two pixels.
Accordingly, the object of this invention is to provide an apparatus which is simple in structure and can operate at high speed to detect the similarity between pixels, and also an apparatus which is simple in structure and can generate interpolation signals, both apparatuses being capable of cooperating to form a high-quality image.